In response to relatively recent federal and state "clean air" regulations, carburetor limiter caps have been used to restrict carburetor fuel flow metering valve adjustment to prevent the excessive emission of carbon monoxide and unburned hydrocarbons from internal combustion engine. Primarily, limiters have been used with conventional float bowl carburetors to control automobile exhaust emissions. More recently their use has been extended to diaphragm-type carburetors in small engines simply to prevent gross misadjustment of fuel flow. However, future emissions regulations are expected to extend the role of limiter caps to control engine emissions.
Fuel flow within a carburetor is commonly metered during no load or idle engine operation by an "idle" or "low speed" needle valve and during part of full load operation by "main" or "high speed" needle valve. Typically, each valve has a threaded cylindrical body with an enlarged knurled head at one end and a conical or needle shaped valve control surface at the opposite end which is received within an opening in the carburetor body. To calibrate fuel flow, each valve is rotatively adjusted to axially extend or retract the valve control surface within a fuel passage in the carburetor until optimum fuel flow through the passage is achieved. Pre-calibration of the carburetor on a flow test bench may be performed prior to being assembled to an engine. After assembly to an engine, it is customary to adjust the metering valves, if needed, to fine tune fuel flow to actual engine demand. Subsequent improper over adjustment (either too rich or too lean) of fuel flow by the engine-powered-appliance-end-user is prevented by affixing a limiter cap over the head of each valve.
These limiter caps generally consist of a cylindrical body having an opening at one end for axially receiving the valve head in tight fitting engagement to prevent removal and ensure rotation of both in unison. A recess in the opposite end of the cap is provided to enable an adjustment tool to engage the valve directly or the cap alone to rotate both in unison to make fuel flow adjustments. Projecting radially outwardly from the cap body is an arm for abutting against a fixed stop extending from the carburetor to limit valve rotation. Stop members such as an integrally cast projection of the carburetor or the body of another cap press-fit on an adjacent needle valve may be used to limit valve and cap rotation and hence adjustment. Removal and reorientation of the limiter cap, after calibration with the cap secured to the valve, is intentionally made impractical, if not impossible, for the end user by tamper proof cap construction that requires the application of considerable force to remove the limiter, possibly damaging or destroying the cap.
In the case of two-stroke cycle engines such limiter caps prevent the fuel flow adjustment range to be incorrectly set by the subsequent end-user, preventing over adjustment toward rich, that could increase emissions above clean-air standard, and also preventing over adjustment toward lean that could deprive the engine of lubrication entrained in the fuel flow, thereby leading to overheating or even catastrophic failure. However, the limited adjustment range permitted by the limiter cap does enable a user or operator of the power tool to adjust the necessary range of fuel flow to keep the engine efficiently operating under the full range of temperature, humidity, altitude or other engine operating conditions which may be encountered.
During manufacture of the carburetor, and also during subsequent assembly of the carburetor to the engine by the engine manufacturer, assembly and proper orientation of these limiter caps is difficult and requires considerable dexterity. If improperly oriented, its tamper proof construction virtually prevents removal without damaging the cap and disturbing the optimum fuel flow setting of the valve.
U.S. Pat. No. 5,236,634 Hammett et al ('634) and U.S. Pat. No. 5,322,645 Hammett et al ('645), both assigned to Walbro Corporation (assignee of record herein), disclose and claim improvements in limiter caps and methods of adjusting fuel flow which successfully overcome such problems, and are incorporated herein by reference.
The limiter caps of the '634 and '645 patents have operated successfully in commercial use to restrict adjustment of a valve to prevent excessive engine exhaust emissions and engine overheating or failure. They facilitate quick and easy assembly of the cap to a needle valve or a carburetor body and final calibration of the carburetor while operating on an engine without requiring the removal of the grommet and engine shroud after final carburetor calibration. These limiter caps may be individually installed after initial calibration of an assembled carburetor on a flow test bench and prior to performing final engine factory calibration of the carburetor on an engine.
They also allow assembly of the limiter cap onto a needle valve of the carburetor to enable rotational adjustment of each valve during carburetor calibration, simple and accurate positioning of the arm of each cap relative to the final adjusted positioned of the valve and carburetor stops, and easy assembly of the cap into secure locking engagement with the valve to allow rotation of the cap and valve only in unison while limiting rotational adjustment of the valve in either direction.
After being locked on they allow limited fuel flow adjustment to enable a user of an engine powered tool to adequately adjust carburetor performance to fine tune engine operation under a variety of operating conditions while preventing fuel flow over adjustment which otherwise could cause excessive exhaust gas emissions or engine overheating. The prepositioning feature allows quick and easy limiter arm orientation, after the caps are mounted in a freely rotating position on the valve, to expediently, yet accurately, fix the allowable range of valve rotation. Another advantage is that the cap may be carried on the valve during assembly without dislodging or vibrating free.
Despite the numerous features and advantages of the limiter cap and methods of adjusting fuel flow of the invention as disclosed and claimed in the aforementioned '634 and '645 patents, there nevertheless remained the longstanding and ongoing need to further reduce manufacturing and material costs of both the limiter caps and associated needle valves, to further simplify, facilitate and render more economical the handling, shipment, storage and installation of such caps on the associated needle valves as well as the adjustment of fuel flow using the needle valve, all without substantially modifying the outer shape and configuration of the type of limiter caps of the '634 and '645 patents. There was also an ongoing need to improve the function and operation of the limiter cap in association with the needle valve and to render the same more versatile as to choice of material usable in constructing the limiter cap. In addition there was the longstanding and overriding need to improve the construction of such limiter caps to enhance their tamper proof characteristics to meet present and proposed governmental and industry standards in this regard. There was also a need to be able to remove the caps, but only by authorized personnel, and without damaging the caps/or needle valves.
The improvements disclosed and claimed in the aforementioned parent application Ser. No. 08/696,693, filed Aug. 14, 1996, now U.S. Pat. No. 5,753,148 also assigned to Walbro Corporation (assignee of record herein), and which application is also incorporated herein by reference, provide improved limiter cap, needle valve, and cap orientor constructions and improved methods of utilizing the same, in the form of various alternative and/or cooperatively combinable embodiments, which satisfy the aforementioned needs, while still satisfying most if not all of the objects and retaining the describe features and advantages of the limiter cap embodiments and methods of the aforementioned '634 and '645 patents.
The improved limiter cap of the aforesaid parent application is of two-piece construction comprising a hollow cylindrical outer body carrying the limiter arm and a spring material retainer clip telescopically received within the outer body. The retainer clip is in the form of a hollow sleeve provided with inwardly and outwardly protruding resilient barbs reversely oriented relative to one another to respectively engage the cap body and the needle valve shank to respectively prevent, on the one hand, retrograde relative telescopic motion between the clip and the body, and on the other hand, between the clip and valve shank. Preferably the clip sleeve is split lengthwise to define a parting gap therein, and the sleeve has a free state diameter greater than that of the body so as to be readily compressible to ensmall the sleeve diameter to facilitate telescopic insertion of the sleeve into the cap body passage.
Due to this two-piece construction the limiter cap retainer clip can be made of spring metal material whereas the cap body can be made of either relatively rigid plastic material or metal. By transferring the resilient, spring locking function from the cap body plastic material to the metal retainer clip, less press-on force is required to telescope the limiter cap subassembly onto the needle valve shank, but the limiter cap can not be removed from the needle, except by authorized personnel using a special tool, without destroying the cap. Moreover, if the cap body is made of metal material, even destructive removal is forestalled.
The foregoing two-piece limiter cap construction is provided in one embodiment as a single stage cap for installation only to a locked-on position after engine factory fine tune adjustment with the cap off. In other embodiments a two stage type cap is provided for preassembly to the needle valve to a first position, allowing presetting paired caps to a rich-rich position, while permitting rotational adjustment of the needle valve during engine fine turning. After such adjustment the cap or caps are then pushed further onto the needle to lock the caps and needle for co-rotation to thereby define a predetermined and more limited end-user range of rotational adjustment of the needle valves. The seating of the single or two-stage caps in their locked first and/or second stage positions is made apparent to the installer by an audible click as the inwardly protruding spring barb(s) snap into a needle shank groove after riding over the needle head, and with a two-stage cap, subsequently riding over a second stage retaining shoulder on the needle shank.
To further facilitate engine customer installation of paired low and high speed limiter caps (of both the '634/'635 patent type as well as those of the aforesaid parent application) on the associated side-by-side carburetor installation of low and high speed needle valves, the invention of the parent application further provides various embodiments of "peanut clip" cap orientors and retainers. Both of the cap bodies are individually telescopically inserted into the peanut clip so that it encircles the cap bodies and spans a space therebetween to securely and conveniently hold the caps in a paired side-by-side subassembly for storage, shipment and/or telescopic installation and rotational orientation of the caps simultaneously on their respective needle valve shanks while still held by the peanut clip. The peanut clip then may be removed from the caps once the same are installed in final position, or the clip may be permanently retained on the caps as by orienting the cap limiter arms to capture the peanut clip therebetween by a flanking relationship to the cap limiter arms. The peanut clip is constructed to permit individual limited-range rotation of the caps for end-user engine tuning adjustment while also sufficiently restraining cap rotation so that needle settings are retained by clip restraint of the caps, either supplemental to or in lieu of the usual needle springs, to thereby prevent undesired rotation of the needles induced by engine operation vibration.
Preferably, for use with two-stage type limiter caps, one embodiment of the aforesaid peanut clip is constructed with a stop leg that ensures that initial push-on assembly of the subassembly of peanut clip and paired cap bodies held therein onto the needle ends is automatically stopped at the first stage installation position. After engine fine tuning adjustment by the engine manufacturer with the caps in their first stage position, the caps are directly pushed further within the clip into their locked second stage position while the clip is maintained in its initial position by its stop leg continuing to abut the carburetor body. The stop leg clip also has cap limiter arm entrapment extensions for locking the caps angularly in rich-rich orientation both prior to and after installation of the cap/clip subassembly to its first stage needle-installed position. When the caps are pushed further into the clip, from first to second stage position, the cap limiter arms are then clear of the clip extensions so that the caps (and associated needle valves) can be rotated through their limited adjustment range established by operation of the cap limiter arms.
The peanut clip may be a continuous loop of resilient but non-elastic material in which the clip peanut shape provides individual cap body gripping action for holding the caps in spaced parallel and pre-aligned relationship but also enables flexible deformation of the clip to accommodate unlocking override of orienting ribs and/or interengaging splines of the clip and cap body. In one form of the stop leg clip embodiment a parting gap is provided in the clip opposite the stop leg to thereby form cantilever spring legs to impart resilient deformability to the clip.
Improved forms of needle valves with shank grooves and cooperating barb retaining shoulders are also disclosed and claimed in the parent application that cooperate with the aforesaid improved limiter caps. These needle valves also have a cap abutment conical shoulder against which the inner end of the cap seats in the fully installed position to thereby hinder any improper attempt to pry off the cap with a screw driver blade.
Despite the numerous features and advantages of the several embodiments of the improved two-piece limiter caps, cooperative one-piece shouldered head needle valves and orientor peanut clips as disclosed and claimed in the aforesaid parent application, there nevertheless again remained the longstanding need to even further reduce manufacturing, material, installation and inventory costs of the improved one-piece shouldered head needle valves that cooperate with the improved two-piece limiter caps. It has also been found that there is a need to enhance the performance of the improved stop leg peanut clip embodiment that is used with the aforementioned two-stage needle valves and caps.